I don't know enough about them to say if they are worth it, but Bushmaster makes a $400-ish piston system that can be used in place of the gas system on a typical AR. Build an with the system, and you can likely keep your cost under $1000 (parts build an economical AR minus the cost of the parts you don't need (as they are replaced by the piston system - like the gas tube/gas block, etc.), plus the cost of the piston conversion system). Midway had a sale price of $399 IIRC on the Bushy gas conversion system a couple days ago, probably still in effect. I don't know if that is a competitive price on the system or not, but it is a reference point.

I bought a Sig556 (it's piston-driven action) and soon after bought an AR as I wanted the parts interchangeability and options that the AR platform offers. I considered selling the Sig, but then I cleaned it and remembered how easy it is to clean, what a nice quality the components are, and how low the market is right now...so I have decided to keep it.

BTW - nice avatar!

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(The Joker)